The instant invention pertains to a superior process for making 2H-benzotriazole UV absorbers which are substituted by a perfluoroalkyl group, i.e. trifluoromethyl, usually at the 5-position of the benzo ring.
Japanese TOKU-KAI-Hei 3-57690 generically discloses compounds where the benzo ring of the benzotriazole may be substituted by a host of groups including hydrogen, alkyl, alkoxy, aryloxy, halogen, substituted amino, cyano, nitro, acyl and trihalomethyl. The only specific benzotriazole compounds mentioned are those where the benzo ring is unsubstituted or is substituted at the 5-position by a chloro group. There is no evidence that the Japanese inventors made any trihalomethyl substituted benzotriazole.
German Patent Application 116,230 describes inter alia the preparation of 5-trifluoromethyl-2-(2-hydroxy-5-methylphenyl)-2H-benzotriazolyl-1-oxide. The only synthesis conditions disclosed for the entire group of compounds prepared show the diazotization of the appropriate o-nitroaniline with aqueous sodium nitrite and hydrochloric acid. The German workers offer no synthetic details or more importantly no yield information for the preparation of 5-trifluoromethyl-2-(2-hydroxy-5-methylphenyl)-2H-benzotriazolyl- 1-oxide.
In British Patent Application 2,319,035 and United States Pat. No. 5,977,219, all benzotriazole compounds containing a trifluoromethyl moiety at the 5-position of the benzo ring are referenced to the synthetic procedure of Example 1. Issues to be considered with this synthetic procedure are (a) a 100% excess of the diazonium salt relative to phenol is used; (b) the monoazo prepared by this method is described as a paste (generally materials with the consistency of a paste are impure); the pure monoazo is a solid with a melting point of 101-105xc2x0 C.; (c) the yield of benzotriazole based on the phenol is 11% and is only 5.5% based on the CF3-substituted o-nitroaniline; (d) the diazotization preparation in Example 1 uses concentrated hydrochloric acid; (e) a paper in the J. Org. Chemistry, 1985, (50) 3612 indicates that the reaction of 4-trifluoromethyl-2-nitro aniline with hydrochloric acid can lead to the formation of 4-trifluoromethyl-2-chloroaniline. Such a reaction could at least partly account for the low yields seen with the use of concentrated hydrochloric acid in the diazotization step.
The object of the invention is to provide a facile and improved process for the preparation of 5-perfluoroalkyl substituted 2H-benzotriazole UV absorbers.
By contrast, the instant process describes an improved process for the preparation of 5-perfluoroalkyl (preferably trifluoromethyl) substituted 2H-benzotriazoles where in the diazotization step aqueous alkali metal (preferably sodium) nitrite and concentrated hydrochloric acid are replaced by aqueous alkali metal (preferably sodium) nitrite and concentrated sulfuric acid; and most preferably where aqueous alkali metal (sodium) nitrite and concentrated sulfuric acid are replaced with anhydrous nitrosylsulfuric acid with concentrated sulfuric acid as a diluent to allow operation at safe concentrations.
The instant invention more specifically pertains to a process for preparing a compound of formula I 
wherein
G1 is hydrogen or chloro,
G2 is perfluoroalkyl of 1 to 12 carbon atoms,
E1 is hydrogen, straight or branched chain alkyl of 1 to 24 carbon atoms, straight or branched chain alkenyl of 2 to 24 carbon atoms, cycloalkyl of 5 to 12 carbon atoms, phenylalkyl of 7 to 15 carbon atoms, phenyl, or said phenyl or said phenylalkyl substituted on the phenyl ring by one to three alkyl of 1 to 4 carbon atoms; or E1 is alkyl of 1 to 24 carbon atoms substituted by one or two hydroxy groups,
E2 is straight or branched alkyl chain of 1 to 24 carbon atoms, straight or branched chain alkenyl of 2 to 18 carbon atoms, cycloalkyl of 5 to 12 carbon atoms, phenylalkyl of 7 to 15 carbon atoms, phenyl, or said phenyl or said phenylalkyl substituted on the phenyl ring by one to three alkyl of 1 to 4 carbon atoms; or E2 is said alkyl of 1 to 24 carbon atoms or said alkenyl of 2 to 18 carbon atoms substituted by one or more xe2x80x94OH, xe2x80x94OCOE11, xe2x80x94OE4, xe2x80x94NCO, xe2x80x94NHCOE11 or xe2x80x94NE7E8, or mixtures thereof, where E4 is straight or branched chain alkyl of 1 to 24 carbon atoms; alkenyl of 2 to 18 carbon atoms; or said alkyl or said alkenyl interrupted by one or more xe2x80x94Oxe2x80x94, xe2x80x94NHxe2x80x94or xe2x80x94NE4xe2x80x94 groups or mixtures thereof and which can be unsubstituted or substituted by one or more xe2x80x94OH, xe2x80x94OE4 or xe2x80x94NH2 groups or mixtures thereof; or E2 is xe2x80x94(CH2)mxe2x80x94COxe2x80x94E5;
E5 is OE6 or NE7E8, or
E5 is xe2x80x94PO(OE12)2, xe2x80x94OSi(E11)3 or xe2x80x94OCOxe2x80x94E 1, or straight or branched chain C1-C24alkyl which can be interrupted by xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or xe2x80x94NE11 and which can be unsubstituted or substituted by xe2x80x94OH or xe2x80x94OCOxe2x80x94E11, C5-C12 cycloalkyl which is unsubstituted or substituted by xe2x80x94OH, straight chain or branched C2-C18alkenyl which is unsubstituted or substituted by xe2x80x94OH, C7-C15aralkyl, xe2x80x94CH2xe2x80x94CHOHxe2x80x94E13 or glycidyl,
E6 is hydrogen, straight or branched chain C1-C24alkyl which is unsubstituted or substituted by one or more OH, OE4 or NH2 groups, or xe2x80x94OE6 is xe2x80x94(OCH2CH2)wOH or xe2x80x94(OCH2CH2)wOE21where w is 1 to 12 and E21 is alkyl of 1 to 12 carbon atoms,
E7 and E8 are independently hydrogen, alkyl of 1 to 18 carbon atoms, straight or branched chain alkenyl of 2 to 18 carbon atoms, straight or branched chain C3-C18alkyl which is interrupted by xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or xe2x80x94NE11xe2x80x94, C5-C12cycloalkyl, C6-C14aryl or C1-C3hydroxylalkyl, or E7 and E8 together with the N atom are a pyrrolidine, piperidine, piperazine or morpholine ring,
E5 is xe2x80x94Xxe2x80x94(Z)pxe2x80x94Yxe2x80x94E15 wherein
X is xe2x80x94Oxe2x80x94 or xe2x80x94N(E16)xe2x80x94,
Y is xe2x80x94Oxe2x80x94 or xe2x80x94N(E17)xe2x80x94,
Z is C2-C12-alkylene, C4-C12-alkylene interrupted by one to three nitrogen atoms, oxygen atoms or a mixture thereof, or is C3-C12-alkylene, butenylene, butynylene, cyclohexylene or phenylene, each substituted by a hydroxyl group,
m is zero, 1 or 2,
p is 1, or p is also zero when X and Y are xe2x80x94N(E16)xe2x80x94 and xe2x80x94N(E17)xe2x80x94, respectively,
E15 is a group xe2x80x94COxe2x80x94C(E18)=C(H)E19 or, when Y is xe2x80x94N(E17)xe2x80x94, forms together with E17 a group xe2x80x94COxe2x80x94CHxe2x95x90CHxe2x80x94COxe2x80x94, wherein E18 is hydrogen or methyl, and E19 is hydrogen, methyl or xe2x80x94COxe2x80x94Xxe2x80x94E20, wherein E20 is hydrogen, C1-C12-alkyl or a group of the formula 
xe2x80x83wherein the symbols E1, G2, X, Z, m and p have the meanings defined above, and E16 and E17 independently of one another are hydrogen, C1-C12-alkyl, C3-C12-alkyl interrupted by 1 to 3 oxygen atoms, or is cyclohexyl or C7-C15aralkyl, and E16 together with E17 in the case where Z is ethylene, also forms ethylene,
E11 is hydrogen, straight or branched chain C1-C18alkyl, C5-C12cycloalkyl, straight or branched chain C2-C18alkenyl, C6-C14aryl or C7-C15aralkyl,
E12 is straight or branched chain C1-C18alkyl, straight or branched chain C3-C18alkenyl, C5-C10cycloalkyl, C6-C16aryl or C7-C15aralkyl, and
E13 is H, straight chain or branched C1-C18alkyl which is substituted by xe2x80x94PO(OE12)2, phenyl which is unsubstituted or substituted by OH, C7-C15aralkyl or xe2x80x94CH2OE12, which comprises
diazotizing a perfluoroalkyl substituted o-nitroaniline of formula II 
xe2x80x83using concentrated sulfuric acid and an alkali metal nitrite (preferably sodium nitrite) or nitrosylsulfuric acid (most preferably nitrosylsulfuric acid) to form the corresponding
diazonium salt of formula III 
which then couples with a phenol of formula IV 
to form a monoazobenzene compound of formula V 
reducing the monoazobenzene intermediate of formula V to the corresponding 2H-benzotriazole compound of formula I by conventional reduction means; and
with the proviso that when concentrated sulfuric acid and alkali metal nitrite are used, E1 and E2 are alkyl of 1 to 4 carbon atoms; or E1 can also be hydrogen.
Preferably, the instant process involves the preparation of a compound of formula 
which comprises
diazotizing a substituted o-nitroaniline compound of formula IIa 
using concentrated sulfuric acid and sodium nitrite or nitrosylsulfuric acid to form the diazonium salt of formula IIIa 
which then couples with a phenol of formula IV 
to form the corresponding monoazobenzene compound of formula Va 
reducing the monoazobenzene intermediate of formula Va to the corresponding 2H-benzotriazole compound of formula Ia by conventional reduction means; and
with the proviso that when concentrated sulfuric acid and alkali metal nitrite are used, E1 and E2 are alkyl of 1 to 4 carbon atoms; or E1 can also be hydrogen.
Preferably, in the compound of formula I,
G1 is hydrogen,
G2 is CF3xe2x80x94,
E1 is phenylalkyl of 7 to 15 carbon atoms, phenyl, or said phenyl or said phenylalkyl substituted on the phenyl ring by one to three alkyl of 1 to 4 carbon atoms,
E2 is straight or branched alkyl chain of 1 to 24 carbon atoms, straight or branched chain alkenyl of 2 to 18 carbon atoms, cycloalkyl of 5 to 12 carbon atoms, phenylalkyl of 7 to 15 carbon atoms, phenyl, or said phenyl or said phenylalkyl substituted on the phenyl ring by one to three alkyl of 1 to 4 carbon atoms; or E2 is said alkyl of 1 to 24 carbon atoms or said alkenyl of 2 to 18 carbon atoms substituted by one or more xe2x80x94OH, xe2x80x94OCOE11, xe2x80x94OE4, xe2x80x94NCO, xe2x80x94NH2, xe2x80x94NHCOE11, xe2x80x94NHE4 or xe2x80x94N(E4)2, or mixtures thereof, where E4 is straight or branched chain alkyl of 1 to 24 carbon atoms; or said alkyl or said alkenyl interrupted by one or more xe2x80x94Oxe2x80x94, xe2x80x94NHxe2x80x94 or xe2x80x94NE4xe2x80x94 groups or mixtures thereof and which can be unsubstituted or substituted by one or more xe2x80x94OH, xe2x80x94OE4 or xe2x80x94NH2 groups or mixtures thereof; or
is a compound of formula I wherein,
G1 is hydrogen,
G2 is CF3xe2x80x94,
E1 is hydrogen or straight or branched alkyl of 4 to 24 carbon atoms, and
E2 is as defined above.
Preferably, the compound of formula I is also where
G1 is hydrogen,
G2 is is CF3xe2x80x94,
E1 is hydrogen, straight or branched alkyl of 4 to 24 carbon atoms or phenylalkyl of 7 to 15 carbon atoms,
E2 is xe2x80x94(CH2)mxe2x80x94COxe2x80x94E5,
E5 is xe2x80x94OE6 or xe2x80x94NE7E8, or
E5 is
xe2x80x94Xxe2x80x94(Z)pxe2x80x94Yxe2x80x94E15
wherein
X is xe2x80x94Oxe2x80x94 or xe2x80x94N(E16)xe2x80x94,
Y is xe2x80x94Oxe2x80x94 or xe2x80x94N(E17)xe2x80x94,
Z is C2-C12-alkylene, C4-C12-alkylene interrupted by one to three nitrogen atoms, oxygen atoms or a mixture thereof, or is C3-C12-alkylene, butenylene, butynylene, cyclohexylene or phenylene, each substituted by a hydroxyl group,
m is 0, 1, 2 or 3,
p is 1, or p is also zero when X and Y are xe2x80x94N(E16)xe2x80x94 and xe2x80x94N(E17)xe2x80x94, respectively,
E15 is a group xe2x80x94COxe2x80x94C(E18)xe2x95x90C(H)E19 or, when Y is xe2x80x94N(E17)xe2x80x94, forms together with E17 a group xe2x80x94COxe2x80x94CHxe2x95x90CHxe2x80x94COxe2x80x94, wherein E18 is hydrogen or methyl, and E19 is hydrogen, methyl or xe2x80x94COxe2x80x94Xxe2x80x94E20, wherein E20 is hydrogen, C1-C12-alkyl or a group of the formula. 
More preferably, the compound of formula I is
where
G1is hydrogen,
G2 is CF3xe2x80x94,
E1 is phenylalkyl of 7 to 15 carbon atoms, phenyl, or said phenyl or said phenylalkyl substituted on the phenyl ring by one to three alkyl of 1to 4 carbon atoms,
E2 is straight or branched alkyl chain of 1 to 24 carbon atoms, straight or branched chain alkenyl of 2 to 18 carbon atoms, cycloalkyl of 5 to 12 carbon atoms, phenylalkyl of 7 to 15 carbon atoms, phenyl, or said phenyl or said phenylalkyl substituted on the phenyl ring by one to three alkyl of 1 to 4 carbon atoms; or E2 is said alkyl of 1 to 24 carbon atoms or said alkenyl of 2 to 18 carbon atoms substituted by one or more xe2x80x94OH, xe2x80x94OCOE11, xe2x80x94NH2 or xe2x80x94NHCOE11, or mixtures thereof, or said alkyl or said alkenyl interrupted by one or more xe2x80x94Oxe2x80x94 and which can be unsubstituted or substituted by one or more xe2x80x94OH; or is a compound of formula I wherein,
G1is hydrogen,
G2 is CF3xe2x80x94,
E1 is hydrogen, straight or branched alkyl of 4 to 24 carbon atoms or phenylalkyl of 7 to 15 carbon atoms, and
E2 is as defined above.
Still more preferably, the compound of formula I is
where
G1 is hydrogen,
G2 is CF3xe2x80x94,
E1 is hydrogen, straight or branched alkyl of 4 to 24 carbon atoms or phenylalkyl of 7 to 15 carbon atoms,
E2 is (CH2)mxe2x80x94COxe2x80x94E5,
E5 is xe2x80x94OE6 or xe2x80x94NE7E8 where
E6 is hydrogen, straight or branched chain C1-C24alkyl which is unsubstituted or substituted by one or more OH groups, or xe2x80x94OE6 is xe2x80x94(OCH2CH2)wOH or xe2x80x94(OCH2CH2)wOE21where w is 1to 12 and E21is alkyl of 1to 12 carbon atoms, and
E7 and E8 are independently hydrogen, alkyl of 1to 18 carbon atoms, straight or branched chain C3-C18alkyl which is interrupted by xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or xe2x80x94NE11xe2x80x94, C5-C12cycloalkyl, C6-C14aryl or C1-C3hydroxylalkyl, or E7 and E8 together with the N atom are a pyrrolidine, piperidine, piperazine or morpholine ring.
Illustrative of the compounds of formula I which can be made by the instant process are
(a) 5-trifluoromethyl-2-(2-hydroxy-3-(xcex1-cumyl-5-tert-octylphenyl)-2H-benzotriazole;
(b) 5-trifluoromethyl-2-(2-hydroxy-5-tert-octylphenyl)-2H-benzotriazole;
(c) 5-trifluoromethyl-2-(2-hydroxy-3,5-di-tert-octylphenyl)-2H-benzotriazole;
(d) 5-trifluoromethyl-2-[2-hydroxy-5-(2-hydroxyethyl)phenyl]-2H-benzotriazole;
(e) 5-trifluoromethyl-2-(2-hydroxy-3,5-di-xcex1-cumylphenyl)-2H-benzotriazole;
(f) 3-(5-trifluoromethyl-2H-benzotriazol-2-yl)-5-tert-butyl-4-hydroxyhydrocinnamic acid;
(g) methyl 3-(5-trifluoromethyl-2H-benzotriazol-2-yl)-5-tert-butyl-4-hydroxyhydrocinnamate;
(h) isooctyl 3-(5-trifluoromethyl-2H-benzotriazol-2-yl)-5-tert-butyl-4-hydroxyhydrocinnamate;
(i) 5-trifluoromethyl-2-[2-hydroxy-5-(3-hydroxypropyl)phenyl]-2H-benzotriazole;
(j) 5-trifluoromethyl-2-[2-hydroxy-5-(3-acryloyloxypropyl)phenyl]-2H-benzotriazole;
(k) 5-trifluoromethyl-2-[2-hydroxy-5-(3-methacryloyloxypropyl)phenyl]-2H-benzotriazole;
(l) 5-trifluoromethyl-2-[2-hydroxy-5-(3-acrylylaminopropyl)phenyl]-2H-benzotriazole;
(m) 5-trifluoromethyl-2-[2-hydroxy-5-(3-methacrylylaminopropyl)phenyl]-2H-benzotriazole;
(n) 5-trifluoromethyl-2-(2-hydroxy-3-x-cumyl-5-tert-butylphenyl)-2H-benzotriazole;
(o) 5-trifluoromethyl-2-(2-hydroxy-3-x-cumyl-5-nonylphenyl)-2H-benzotriazole;
(p) 5-trifluoromethyl-2-[2-hydroxy-3-(x-cumyl-5-(2-hydroxyethyl)phenyl]-2H-benzotriazole;
(q) 5-trifluoromethyl-2-[2-hydroxy-3-ox-cumyl-5-(3-hydroxypropyl)phenyl]-2H-benzotriazole;
(r) 5-trifluoromethyl-2-(2-hydroxy- 3,5-ditert-amylphenyl)-2H-benzotriazole;
(s) 5-trifluoromethyl-2-(2-hydroxy- 3,5-ditert-butylphenyl)-2H-benzotriazole;
(t) 5-trifluoromethyl-2-(2-hydroxy-3-dodecyl-5-methylphenyl)-2H-benzotriazole;
(u) 5-trifluoromethyl-2-[2-hydroxy-3-tert-butyl-5-(3-hydroxypropyl)phenyl)-2H-benzotriazole; and
(v) 5-trifluoromethyl-2-[2-hydroxy-3-tert-butyl-5-(2-hydroxyethyl)phenyl]-2H-benzotriazole;
Most preferably, the instant process involves the preparation of a compound of formula Ib, which comprises 
diazotizing a substituted o-nitroaniline compound of formula IIa 
using nitrosylsulfuric acid to form the diazonium salt of formula IIIa 
which then couples with a phenol of formula IVa 
to form the corresponding monoazobenzene compound of formula Vb 
reducing the monoazobenzene intermediate of formula Vb to the corresponding 2H-benzotriazole compound of formula Ib by conventional reduction means.
Most preferably, the instant process involves the preparation of a compound of formula Ic, which comprises 
diazotizing a substituted o-nitroaniline compound of formula IIa 
using nitrosylsulfuric acid to form the diazonium salt of formula IIIa 
which then couples with a phenol of formula IVa 
to form the corresponding monoazobenzene compound of formula Vc 
reducing the monoazobenzene intermediate of formula Vc to the corresponding 2H-benzotriazole compound of formula Ic by conventional reduction means.
Ia. In the process for making the diazonium salts using a perfluoroalkyl substituted o-nitroaniline (i.e. 4-trifluoromethyl-2-nitroaniline, CF3xe2x80x94ONA), sulfuric acid and an aqueous alkali metal nitrite (i.e. sodium nitrite) solution, the following process parameters pertain:
a. The molar ratio of CF3xe2x80x94ONA:sulfuric acid is 1:10 to 1:1; preferably 1:5 to 1:1; and most preferably 1:2-3.5.
b. The molar ratio of CF3xe2x80x94ONA:sodium nitrite is 1:1to 1:4; preferably 1:1to 1:2; most preferably 1:1.
c. The temperature used for this reaction is from xe2x88x9230xc2x0 C. to 50xc2x0 C.; preferably from xe2x88x9220xc2x0 C. to 20xc2x0 C.; most preferably from xe2x88x9210xc2x0 C. to 5xc2x0 C.
lb. In the process for making the diazonium salts using a perfluoroalkyl substituted o-nitroaniline (i.e. 4-trifluoromethyl-2-nitroaniline, CF3xe2x80x94ONA) and nitrosylsulfuric acid in sulfuric acid, the following process parameters pertain:
a. The molar ratio of CF3xe2x80x94ONA:nitrosylsulfuric acid is 1:1to 1:2; preferably 1:1to 1:1.2; and most preferably 1:1.
b. The molar ratio of CF3xe2x80x94ONA:sulfuric acid is 1:1to 1:10; preferably 1:2 to 1:7; most preferably 1:2 to 1:5.
c. The temperature used for this reaction is from xe2x88x9230xc2x0 C. to 50xc2x0 C.; preferably from xe2x88x9220xc2x0 C. to 40xc2x0 C.; most preferably from 0xc2x0 C. to 25xc2x0 C.
When preparing a diazonium salt using nitrosylsulfuric acid, a very low amount of water is required. The system is essentially anhydrous. When sulfuric acid concentrations are under 90%, nitrosylsulfuric acid becomes nitric oxide (NO) and evolves as a gas before it has time to react with the CF3xe2x80x94ONA. At the end of the diazotization reaction, the diazonium salt solution in sulfuric acid is diluted with water to about 20-25%.
II. For the preparation of the monoazobenzene intermediate, there are two different coupling methods possible. The alkaline coupling method is described in detail in U. S. Pat. Nos. 4,275,004 and 4,347,180 which are incorporated herein by reference.
The acidic coupling process is described in detail in U.S. Pat. No. 5,436,322 which is incorporated herein by reference.
It is noted that instant Example 9 shows a coupling method which neither strongly alkaline nor strongly acidic. Rather, this Example shows coupling which is buffered with acetic acid and sodium hydroxide.
The details of the more preferred acidic coupling method are described infra.
The diazonium salt formed as described above is reacted with the appropriate phenol in a solvent containing a surface active modifier at a temperature of xe2x88x9230xc2x0 C. to 75xc2x0 C.; preferably at xe2x88x9220xc2x0 C. to 50xc2x0 C.; most preferably at xe2x88x9210xc2x0 C. to 35xc2x0 C.
The solvents used are water, an aromatic hydrocarbon, an aliphatic hydrocarbon or a mixture thereof. Preferably, the solvent is water, toluene, o-xylene, m-xylene, p-xylene or a mixture of said xylenes, mesitylene, pseudocumene, hexane, heptane, octane, nonane or a mixture thereof. Most preferably, the solvent is water, toluene, o-xylene, m-xylene, p-xylene, a mixture of said xylenes, heptane or a mixture thereof.
The amount of solvent to be used is that sufficient to dissolve the reactants. The amount of solvent is not critical, but making the solution too dilute is to be avoided.
The surface active modifier to be used is any one or a mixture of materials selected from the group consisting of emulsifying agents, surfactants, phase transfer agents and dispersants.
Preferably, the surfactive modifier is HOSTAPUR(copyright) SAS93 (Hoechst) or PETROSUL(copyright) M-60 (Penreco). The amount used is that needed to ensure adequate mixing of the reactants.
The molar ratio of diazonium salt:phenol is 2:1 to 1:2; preferably 1.5:1 to 1:1.5; most preferably 1:1.
III. The monoazobenzene compounds prepared in the instant process can be conveniently reduced to the corresponding benzotriazolyl- 1-oxide and then to the corresponding 2H-benzotriazole by any number of conventional reduction methods. An illustrative list of such methods is given below, but should not be construed as being the only methods possible for carrying out said reduction.
1. EP 0380840 A1 describes the hydrogenation of a benzotriazolyl-1-oxide to the benzotriazole using palladium/carbon catalyst in toluene/water and in the presence of dimethylamine.
2. EP 0380840 A1 also discloses the hydrogenation of a benzotriazolyl-1-oxide to the benzotriazole using Raney nickel catalyst in toluene/2-butanol and in the presence of 1,5-diazabicyclo[5.4.0]undecane.
3. EP 0380839 A1 discloses the hydrogenation of a nitromonoazobenzene to the benzotriazole using Raney nickel catalyst in toluene/isopropanol and in the presence of sodium hydroxide.
4. EP 0380839 A1 also discloses the hydrogenation of a nitromonoazobenzene to the benzotriazole using palladium/carbon catalyst in toluene/water/isopropanol and in the presence of dimethylamine.
5. Japanese Sho 37-5934 (1962) and U.S. Pat. No. 3,773,751 describe the reduction of a nitromonoazobenzene to the benzotriazole using zinc, sodium hydroxide in an alcohol.
6. U.S. Pat. No. 2,362,988 discloses a variety of methods for the reduction of a nitromonoazobenzene to a benzotriazole. These include the use of:
a. ammonium sulfide;
b. an alkali metal sulfide;
c. zinc and ammonia;
d. hydrogen sulfide and sodium; or
e. zinc and hydrochloric acid.
7. Japanese Sho 56-133076 (1981) describes the reduction of a nitromonoazo-benzene to a benzotriazole using quinone plus a variety of coreactants. These include:
a. zinc;
b. ammonium sulfide;
c. alkali metal sulfide;
d. alkali metal hydrosulfide; or
e. hydrazine.
8. Japanese Sho 52-113973 (1977) and Sho 52-113974 (1977) describe the hydrogenation of a nitromonoazobenzene to a benzotriazole using a precious metal catalyst in the presence of a base.
9. Japanese Sho 59-170172 (1984) and Sho 63-72682 (1988) describe the reduction of a nitromonoazobenzene to a benzotriazole using a quinone or an aromatic ketone in the presence of an alcohol and a base and with heating.
10. Japanese Sho 61-215378 (1986) describes the reduction of a nitromonoazobenzene or a benzotriazolyl-1-oxide benzotriazole to a benzotriazole using an aldehyde and aromatic ketone in the presence of a base.
11. Japanese Sho 63-72683 (1988) and U.S. Pat. No. 4,780,541 describe the reduction of a nitromonoazobenzene or a benzotriazolyl- 1-oxide benzotriazole to a benzotriazole using a primary or secondary alcohol and an aromatic ketone in the presence of a base.
12. Japanese Sho 63-186886 (1988) describes the electrolytic reduction of a nitromonoazobenzene or a benzotriazolyl-1-oxide benzotriazole to a benzotriazole using an alkali metal hydroxide in water or an aqueous alcohol solution.
13. Japanese Sho 61-215379 (1986) and U.S. Pat. No. 4,789,541 describe the reduction of a benzotriazolyl- 1-oxide benzotriazole to a benzotriazole using an aldehyde and an aromatic ketone in the presence of a base.
14. U.S. Pat. No. 5,571,924 describes the reduction of a nitromonoazobenzene or a benzotriazolyl- 1-oxide benzotriazole to a benzotriazole using hydrazine and a precious metal catalyst.
15. U.S. Pat. No. 3,978,074 discloses the reduction of a nitromonoazobenzene to a benzotriazole using a hydrogen and a noble metal catalyst in the presence of an aqueous alkali metal hydroxide solution.
16. U.S. Pat. No. 4,219,480 discloses the reduction of a nitromonoazobenzene to a benzotriazole using a hydrogen and a Raney nickel catalyst in the presence of an aqueous alkali metal hydroxide solution or in the presence of an aliphatic amine.
17. U.S. Pat. No. 4,230,867 discloses the reduction of a nitromonoazobenzene to a benzotriazole using a hydrogen and a noble metal catalyst in the presence of an aliphatic amine.